That would be challenging. You would need a vacuum switch that opens under no vacuum, and closes under high vacuum. It would need to be adjustable so you could set it to allow operation while cruising, and this would require that you measure the vacuum under different conditions to see what level you would need the switch to trip at. Or, you'd have to drive and adjust for a couple of weeks until it was working the way you wanted. And, it isn't necessary on modern cars, depending on make and model the AC is controlled by the computer, and the computer cuts compressor power under WOT conditions.
Actually wiring it in is easy enough, you just mount the switch near the compressor, cut one of the compressor control wires, attach both ends to the vacuum switch, then run a vacuum line to the intake manifold. You need direct exposure to the intake itself, not a ported line.
On further thought there would probably be no reason to use a vacuum switch just a limit type switch on the throttle to turn it on when the pedal is depressed slightly with an adjustment for dialing it in.
For highway driving I run the air until the car is cold. then I hit the ac button so the fan is only on vent mode. Once the car starts getting hot again I press the ac button again until the car get cool.
I would switch it on and off at every overpass (around every mile) when we were driving through ohio. I ended up getting 27mpg out of a '98 Honda odyssey doing this at 70mph.
2008 EPA adjusted:
Distance traveled by bicycle in 2007= 1,830ish miles
Average commute speed=25mph (yes, that's in a car)